Field of the Invention
The present inventions relate to an actuation system for a high pressure fluid powered device. The invention has particular application to a high pressure impact device.
Description of the Prior Art
Pneumatic drive systems are used in a variety of applications, particularly with regard to tools. Traditionally, pneumatic tools have been designed to be connected to a source of compressed air, such as a stationary air compressor.
While air compressors provide an effectively unlimited supply of compressed air, they do have several disadvantages. In particular, the need to connect a tool to the air compressor via a hose limits the portability of the tool and also the positions into which it can be manoeuvred. Additionally, air compressors are generally expensive and outside the financial means of some users. Further, safety issues arise from having the hoses lying around the work place which may become caught on various objects or trip up persons within the space.
In an attempt to address these problems, several different systems have been developed.
One such system utilises a combustible gas, such as butane, to provide an explosion that drives the tool's operation. Such combustion systems have safety issues of their own given that the tool usually includes a storage device for combustible gas and a combustion source close to each other. The gas and gas cartridges tend to be expensive and only available from select suppliers. Further, the heat and impact of the explosions tend to be hard wearing on the tool causing them to require frequent maintenance. The electrical components are susceptible to failure if the tool is exposed to moisture such as rain. All of these factors add additional costs and an element of inconvenience to the user.
More recently, portable pressure sources have been developed by which a vessel containing a pressurised fluid such as carbon dioxide may be connected via a regulator to a tool traditionally powered by an air compressor. These systems allow the tools to be used in a more portable fashion without being restricted by the hosing requirements of conventional set ups.
However the available pneumatic tools are designed for a pneumatic set up where the supply of compressed air or gas is effectively unlimited. As such, the energy transfer is relatively inefficient, particularly in the drive mechanism.
In particular, the drive mechanisms of such tools have passages and chambers shaped such that excessive space is present—“dead volume” which requires filling during operation of the tool. This requires a larger volume of gas to be used in each operating cycle.
As well as requiring a larger volume of gas to fill the space, this dead volume disrupts the flow of the gas, reducing the efficiency of the energy transfer to the drive mechanism of the tool. As a result, a greater amount of gas is required in order to achieve the desired power output of the tool.
Therefore, using the portable pressurised fluid systems previously discussed generally results in the tool being able to be used only for an impractically low number of repetitions before replacement or replenishment of the fluid vessel is required.
Further, in situations where the fluid is stored in a liquid phase and vaporised to drive the tool, the low temperatures generated by the vaporisation of the fluid causes problems. The tools have a tendency to freeze and malfunction after a certain number of uses and exposure of the operating mechanism of the tool to the pressurised gas. A more efficient energy transfer mechanism would require a smaller volume of gas to be used per operating cycle. This would result in less cooling issues and extend the number of repetitions the tool could perform before freezing.
The noise created by each operation of the tool is also an issue, as it has the potential to cause hearing damage to the user and other people nearby. The noise also adds to noise pollution of the environment, which is at the very least an annoyance, particularly in a residential area. The noise created by the tool's operation and exhaust is related to the volume of gas used. Reducing the volume of gas required may reduce the noise generated by the tool.
It would therefore be an advantage for the drive mechanism of a pneumatic tool to be more efficient in the consumption of gas.
All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.
It is acknowledged that the term ‘comprise’ may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term ‘comprise’ shall have an inclusive meaning—i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term ‘comprised’ or ‘comprising’ is used in relation to one or more steps in a method or process.
It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.
In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art.